Stereoregular polypropylene coated with an insolubilized ethylene oxide polymer



United States Patent STEREGREGULAR PQLYERQPYLENE CQATED W1 lH ANIYSOLUEBILEZED ETHYLENE OXEDE POLYMER George B. Feild, New Castle, Del,assignor to Hercules Incorporated, a corporation of Delaware No Drawing.Filed Set. 4, 1963, Ser- No. 313,800 6 Claims. {CL 117133.8)

This invention relates to polypropylene articles such as fibers,filaments, films, etc having insolubilized on the surface thereof apoly(ethylene oxide) coating and to the process of obtaining an adherentcoating of poly(ethylene oxide) on said polypropylene articles.

At low humidities, many synthetic fibers develop static charge readilywhen rubbed with a second material dif-' fering in electronegativity.The discomfort of an electrical discharge resulting from the developmentof static charge by Walking over carpets made with synthetic fibers isWell known. Development of static charge on clothing contributes toundesirable clinging. Plastic film is often difiicult to handle,particularly at low humidities, because of static charge effects.Plastics and films that develop static charges collect soil readilybecause of the electrostatic attraction for colloidal dirt particles inthe air.

It is well known that poly(ethylene oxide) is an effective antistaticand sizing agent for natural and synthetic fibers. However, the effectis not permanent and, in fact, is only temporary since the poly(ethyleneoxide) is removed by washing and/ or dry-cleaning or is removed bynormal abrasion during use. Articles made of polypropylene, as forexample, fibers, filaments, fabrics, films, etc., are, like othersynthetic materials, subject to static electricity and here the problembecomes even more acute due to the very easy removal of such apoly(ethylene oxide) coating on washing, dry-cleaning or abrasion.

Now in accordance with this invention, it has been discovered that anadherent and relatively permanent coating of an ethylene oxide polymercan be applied to the surface of a polypropylene article by applying tothe surface a mixture of the ethylene oxide polymer and an azidocross-linking agent and heating or irradiating to efiect cross linkingof the ethylene oxide polymer coating. The coating or modified surfaceso obtained is retained even after repeated Washing and/ ordry-cleaning, etc.

It has recently been discovered that polypropylene can be cross-linkedby treatment With azido cross-linking agents but it was not surprisingto find that an ethylene oxide polymer could be bound to the surface ofa polypropylene article by means of an azido cross-linking agent. It isbelieved that the highly adherent coating is produced due to twomechanisms, cross-linking of the ethylene oxide polymer andcross-linking of the ethylene oxide polymer chains to the polypropylenepolymer chains in the surface of the substrate.

Any azido cross-linking agent can be used in obtaining the adherentcoating onto the polypropylene. An outstanding clsss of azidocross-linking agents that can be used for azidoformates which have thegeneral formula T RtCCNa):

where x is at least 1, preferably from about 1 to about 100, and R is anorganic radical, inert to cross-linking reactions, containing at leastone carbon atom per azidoformate group. Exemplary of these azidoformatesare the alkyl azidoformates such as n-octadecyl azidoformate,tetramethylene bis(azidoformate), pentamethylene-bis (azidoformate); thecyclic alkyl azidoformates such as 3,320,088 Patented May 16, 19572-(1-p-rnethyl-8-yloxy) ethyl azidoformate; the aromatic .azidoformatessuch as phenyl azidoformate, a,a'-p-xylylene bis(azidoformate), 2,2isopropylidene bis(p,p'- phenyl azidoformate); the azidoforniate etherssuch as 2,2 oxydiethyl bis(azidoformate), 2,2oxydipropylbis(azidoformate), 2,2 ethylenedioxydiethylbis(azidoformate), the tetraazidoforrnate of pentaerythritolpropyleneoxide .adduct, the azidoformate thioethers such as2,2'-thiodiethyl-bis(azidoformate), 4,4'-thiodibutyl-bis(azidoformate);etc. Still another class of azido cross-linking agents that can be usedare the aromatic polyazides having the general formula R(N where P. isan aromatic grouping inert to the cross-linking reaction, and x is aninteger greater than 1. Preferably x will be an integer from 2 to 200and R will be selected from the group of organic radicals consisting ofarylene and alkarylene radicals. Exemplary of the arcmatic polyazidesuseful in this invention are m-phenylene diazide, 2,4,6-triazidobenzene,4,4-diphenyl diazide, 4,4'-diphenylmethane diazide, 4,4-diazidodiphenylamine, 4,4'-diazido diphenylsulfone, 2,7-diazidonaphthalene and2,6-diazidoanthraquinone. Thus, any compound having at least one azidogroup in the molecule and preferably two or more can be used as theazido cross-linking agent in this invention.

The amount of the azido cross-linlc ng agent used in the preparation ofthe adherent coatings of this invention can be varied over a wide range.Generally, it will be an amount of from about 0.1% of the weight of theethylene oxide polymer up to as high as 20%, but usually will be fromabout 3 to 15% of the weight of the ethylene oxide polymer.

The cross-linking reaction can be initiated either thermally or byradiation. Thus, the reaction can be intiated by heating the coatedpolypropylene article to a temperature of from about C. up to themelting point of the polypropylene, preferably to a temperature of fromabout 70 C. to about 160 C. and more preferably from about C. to aboutC. When the reaction is initiated by radiation, exposure to a Wavelength of from about 0.01 A. to about 7600 A. and referably from about2000 A. to about 5800 A. is effective. The time required to effect thecross-linking reaction will depend on the cross-linking agent, type ofinitiation used, temperature, etc. Generally for radiation initiation,an exposure period of from about 1 to 30 minutes is used, but muchlonger exposures can be used if desired.

Because some bis(azidoformate) cross-linking agents have an appreciablevapor pressure under the conditions used for thermal initiation,efficiency can be increased by confining the polypropylene article toreduce loss of the cross-linking agent by vaporization from the surface.A molding press operated at low pressures is very convenient forreducing the volatile loss. For a continuous process, the fabric or filmbeing treated can be held between the surfaces of continuous belts ofmetal, rubber or plastic. Other similar methods for reducing volatileloss will be apparent. Use of azidoformate cross-linking agents withlower vapor pressure avoids the need for confining the article to reducevolatile loss.

Any article made of a stereoregular polypropylene, i.e., crystallinepolypropylene sometimes also called isotactic, can be coated by theprocess of this invention.

The ethylene oxide polymers used to form the adherent coating on thesurface of polypropylene articles in accord ance with this invention canbe either a homopolymer of ethylene oxide or a copoly-mer of ethyleneoxide with another alkylene oxide as, for example, propylene oxide,butene-l oxide, cisor trans-butene-Z oxide, etc., Wherein the copolymercontains at least about 40% ethylene oxide. The molecular weight of thepolymer that is used is not critical, the only criterion being that itbecomes in- 3 )lubilized on cross-linking. Generally the polymer willave a molecular weight of about 5,000 and preferably om about 100,000 toabout 1,000,000. Higher molecular eight polymers can be used up to10,000,000 or more,

ut may necessitate application to the polypropylene arti 5 e from themelt rather than from a solution.

The amount of ethylene oxide polymer applied to the olypropylene surfaceto alter the properties thereof can a varied over a wide range and will,of course, depend pon the type of polypropylene article being coated.Thus l the case of fibers, yarns and fabrics made of polypropylie, theamount of coating app'ied to the surface is gen- "ally cited as anadd-on weight and the range will be '0m about 0.01% to about 25% of thetotal weight of Jlypropylene, and preferably the add-on level will be )rmost applications from about 0.02% to about 10%. he amount used will, ofcourse, depend on the desired roperty of the polypropylene article.Thus, in the case f antistatic properties, the amount used will dependconderably on the amount of surface per unit weight of the alypropylenearticle. In the case of films and molded fticles, the amount used willobviously be dependent on 1e thickness of the coating desired ratherthan being cited n the basis of the weight of polypropylene. In anyevent,

nce we are dealing with a surface phenomenon, the

nount of the ethylene oxide polymer coating is more |gially cited interms of thickness and will be anything om a monomolecular layer of thepolymer up to 3 mils t more, but for most practical considerations willbe a lickness of about 5 A. and more preferably from about 20 nulsionscan also be painted, sprayed, etc., onto the poly- 4O ropylene surface,padded on, etc. In the case of films and rbrics, they can be applied bya roll, doctor blade, etc. 'iluents suitable for applying the mixture ofethylene xide polymer and azido cross-linking agent are water, any

16ft organic diluent as, for example, aromatic hydrocarans such asbenzene, toluene, etc., halogenated hydroproduct of this invention. Allparts and percentages are by weight unless otherwise indicated.

Examples 1-7 In Examples 27, a 6.8 oz./sq. yd. abrasive twill with a 2/1weave and a 68 x 44 count made from spun polypropylene fibers Was usedand compared with a cotton broadcloth fabric (3.5 oz./sq. yd. and 136 x68 count) used in Example 1 as a control. All fabrics were laundered toremove any factory finishing agents. In Examples 4, 6 and 7, the fabricwas dipped in an ethylene dlChlOllCle solution and in Example 5 a waterdispersion of poly(ethylene oxide) and 12.4% of an azido crosslinkingagent based on the poly(ethylene oxide) and then was passed throughwringer rolls after which the add-on weights of the coating weredetermined. The fabrics were then heated under nitrogen for 1 hour at140 C., except in Example 6 where the fabric was heated for 1 hour at140 C. between the platens of a press at 472 p.s.i.g. In Example 3 thefabric was treated in the same way except that the azido cross-linkingagent was omitted. The poly (ethylene oxide) used in these examples wasa commercial product having a melt viscosity of 23,000 to 26,000 poisesat 150 C. and a 5% water solution viscosity at 25 C. of 1500 to 2500centipoises, a molecular weight of approximately 600,000. In Example 7there was additionally added to the coating solution 4% by weight of thepoly(ethylene oxide) of a polymerized trimethyl dihydroquinoline as anantioxidant.

A static charge was built up on strips of each fabric by frictionalcontact across metal bars. When the static charge on the fabric reached1,000 volts, the friction-producing source was stopped and the chargeallowed to decay. The discharge time for the charge on each fabricrelative to the discharge time for cotton fabric, which has excellentantistatic properties, was noted. In Examples 3 and 4 it was notpossible to induce a charge greater than 100 volts until after thefabric had been washed. In Example 5, it took 31 seconds for the staticcharge to decay from 1,000 to 200 volts and there was excellentretention of this antistatic propertly after washing as seen from thedata below. Tabulated below are the data for each example showing thetime to decay (in minutes and seconds) from a static charge of 1,000volts to 200 volts after one washing and for Examples 3 to 5 after sixwashings.

TABLE I v I Amount of Antistatic Performance After AntistaticPerformance After Solvent for Applying Cross-Linking Agent Poly(EthyleneOne Washing Six Washings Ex. Poly(Ethylene and Concentration, Oxide)Applied No. Oxide) and Con- Percent by Wt. of to Fabric (PercentrationPoly(E thylene cent by Wt) Initial Final Time Initial Final Time Oxide)Voltage Voltage Voltage Voltage Not treated 1,000 200 1'03" Not trcated1,000 990 10 1 5% in CgILClL None. 7- 8 1, 000 915 25' 1, 000 910 25' 5%in C H Cl 12.4% CMBAF -1 10.2 1,000 200 49" 1, 000 200 1'29" 5% in\VateL... 12.4% CMBAF 7.2 1, 000 200 1'10" 1, 000 200 50" 5% in C2HiCl212.4% TEGBAF L... 8.5 1, 000 200 1 9 s 5% in CzH Clg 12.4% TEGBAF S 6 1,000 200 32" l 1,fcyclohexanedimethyl-bis(azidofornlate). 22,2ethyler1edioxydiethyl-bis (azidoformate) ifbOIlS such as carbontetrachloride, ethylene dichloride, Example 8 fiers, wetting agents,antioxidants, etc., can be added to' 1e solution applied, or inertfillers, dyes, etc., if such are esired in the adherent coating. Manyother variations in be apparent to those skilled in the art.

The following examples will illustrate the process of this tvention andthe outstanding antistatic properties of the The fabric prepared inExample 5, having a decay time of 31 seconds to drop 1,000 to 200 volts,was dry-cleaned using two cleaning sequences, each of which involved onewash with a hydrocarbon solvent and one wash with a chlorinatedhydrocarbon solvent (AATCC Test Method 86-1957T). The decay time afterthis dry-cleaning had increased to only 35 seconds.

In contrast, the fabric prepared in Example 3 where no cross-linkingagent was used, and on which a 1,000 volt charge could not be inducedbefore washing or drycleaning, had a decay time of over 5 minutes todrop from 1,000 volts to 200 volts after only one dry-cleaning sequence.

Example 9 A sample of the polypropylene fabric, described in theforegoing examples, Was treated as described in Examples 4-7, exceptthat the coating solution used was a 10% solution of the poly(ethyleneoxide) in benzene and contained 10% by Weight of the poly(ethyleneoxide) of tetramethylene bis(azidoformate). The add-on was 0.2% ofpoly(ethylene oxide) by weight of the fabric. It Was cured by heatingunder nitrogen for 1 hour at 140 C. This fabric was tested for itsantistatic proper ties by building up a static charge by rubbing itacross the knee ten times and then checking the cigarette ash pick-up.It gave no cigarette ash pick-up even at 1 inch from ashes. It was alsowashed once and was free of static charge as measured by same test. Inthe same test, untreated fabric picked up some ashes at 3 inches and alarge amount of ashes at 1 inch.

Example 10 A sheet of compression molded stereoregular polypropylene (acommercial polypropylene having a reduced specific viscosity of 3.3 asmeasured on a 0.1% solution of the polymer in decahydronaphthalene at atemperature of 135 C.) was dip coated with a 1% solution of poly-(ethylene oxide) in ethylene dichloride and containing 0.1% of4,4-diphenylmethane diazide, i.e., 10% by weight of the poly(ethyleneoxide), and then was air dried. The poly(ethylene oxide) used was acommercial, water-soluble homopolymer having a molecular weight of about600,000. A portion of the coated film was irradiated by exposure to ahigh pressure mercury arc (UV range of 1849 to 4,000 A.) at a distanceof 13 inches for 10 minutes. The cross-linked poly(ethylene oxide)coating was not removed when the surface of the film was scrubbed withwarm water whereas when a portion of the coated film that had not beenirradiated was scrubbed with warm water, the poly (ethylene oxide)coating was completely removed.

Example 11 The process described in Example 4 was repeated except thatinstead of poly(ethylene oxide) there was used a copolymer of ethyleneoxide containing 75% by weight of ethylene oxide and 25% by weight ofpropylene oxide, which copolymer had a molecular weight of about 125,-000. The coated polypropylene fabric so obtained took 1 minute to dropfrom a static charge of 1,000 volts to 200 volts. After six washings thedecay time to drop 6 from 1,000 volts to 200 volts was 1 minute andseconds.

As will be seen from the foregoing examples, the process of thisinvention has resulted in the production of a polypropylene surface withpermanently altered proper ties. The new polypropylene having across-linked coating of an ethylene oxide polymer is, as may be seen,resistant to electrostatic charges and retains this resistance evenafter washing, dry-cleaning, etc. In addition to forming an antistaticfinish on the polypropylene article, the printability of thepolypropylene surface is greatly enhanced, as is also the dryreceptivity. Many other uses for the coated polypropylene articles ofthis invention will be obvious to those skilled in the art, as forexample use in the photographic and printing arts, etc.

What I claim and desire to protect by Letters Patent is:

1. As a new article of manufacture, stereoregular poly propylenesubstrate having a substantially permanent and antistatic coating of anethylene oxide polymer selected from the group consisting ofhomopolymers of ethylene oxide and copolymers of ethylene oxide withanother lower alkylene oxide wherein said copolymer contains at leastabout 40% by weight of ethylene oxide, insolubilized by cross-linkingwith an azido cross-linking agent.

2. The product of claim 1 wherein the ethylene oxide polymer ispoly(ethylene oxide).

3. The product of claim 1 wherein the ethylene oxide polymer is acopolymer of ethylene oxide and propylene oxide.

4. The product of claim 1 wherein the polypropylene substrate ispolypropylene fiber.

5. The product of claim 1 wherein the polypropylene substrate ispolypropylene film.

6. The product of claim 1 wherein the polypropylene substrate ispolypropylene fabric.

References Cited by the Examiner UNITED STATES PATENTS 2,525,691 10/1950Lee et al. 117138.8 X 2,986,507 5/1961 Steck 117-93.31 3,101,989 8/1963Toureille 855 3,140,197 7/1964 Heberlein et a1. 117-93.31 3,211,75210/1965 Breslow 260'349 WILLIAM D. MARTIN, Primary Examiner.

R. HUSACK, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION May 16, 1967Patent No. 3,320,088

George B. Peild It is hereby certified that error appears in the abovenumbered patthat the said Letters Patent should read as ent requiringcorrection and corrected below.

Column 1, line 50, for "not read most line 61, for "for" read are Signedand sealed this lath day of November 1967 (SEAL) Attest: Edward M.Fletcher, It. EDWARD J. BRENNER Commissioner of Patents AttestingOfficer

1. AS A NEW ARTICLE OF MANUFACTURE, STEREOREGULAR POLYPROPYLENESUBSTRATE HAVING A SUBSTANTIALLY PERMANENT AND ANTISTATIC COATING OF ANETHYLENE OXIDE POLYMER SELECTED FROM THE GROUP CONSISTING OFHOMOPOLYMERS OF ETHYLENE OXIDE AND COPOLYMERS OF ETHYLENE OXIDE WITHANOTHER LOWER ALKYLENE OXIDE WHEREIN SAID COPOLYMER CONTAINS AT LEASTABOUT 40% BY WEIGHT OF ETHYLENE OXIDE, INSOLUBILIZED BY CROSS-LINKINGWITH AN AZIDO CROSS-LINKING AGENT.